The purpose of this study is to determine if estrogen deficiency plays a major role in the pathogenesis of the changes in collagent metabolism in postmenopausal women, and whether these changes can be prevented or reversed by estrogen replacement therapy. A new method utilizing stable isotopes for quantifying the dermal synthesis rate of collagen in vivo will be used. We have established the necessary techniques to measure skin collagen synthesis rates using stable isotopes. We have at this point completed the full study in 4 subjects, and an additional 23 subjects have either initiated the study or are enrolled, pending study. Our plans over the next year are to continue to recruit and study the remaining subjects, as well as complete the analysis.